Frank-Jürgen Methner (1),
Leif-Alexander Garbe (2), Richard Glattfelder (1), Philip Wietstock
(1); (1) Technische Universität Berlin, Berlin, Germany; (2) Hochschule
Neubrandenburg, Germany
Packaging (Bottles, Draft, and Cans)
Poster
Absorption of a selection of hop volatiles representing different
polarities and molecular sizes (myrcene, limonene, linalool,
alpha-terpineol, geraniol, t-caryophyllene, alpha-humulene) by crown
cork liner polymers and can coatings was investigated in model systems
and in beer during storage. All volatiles measured were prone to migrate
into the closures, and the absorption in a low-density polyethylene
(LDPE) liner was demonstrated to fit well Fick’s 2nd law of diffusion
for a plane sheet. The extent and rate of diffusion was significantly
dissimilar and was greatly dependent on the nature of the volatile.
Diffusion coefficients were deduced and were from highest to lowest in
cm2/day: limonene, 1.32 × e–5; myrcene, 1.17 × e–5; linalool, 0.84 × e–5; alpha-terpineol, 0.72 × e–5; geraniol, 0.49 × e–5; t-caryophyllene, 0.32 × e–5; alpha-humulene, 0.26 × e–5.
The maximum amounts found at equilibrium were in the order limonene
> alpha-humulene > t-caryophyllene > myrcene >> linalool
> alpha-terpineol > geraniol, although it is noteworthy that the
terpene alcohols only diffused in the liner polymer at a maximum rate of
1.4%, while e.g., limonene was found at an amount of 105.7% as related
to the initial amounts in the beer. Applying an LDPE liner with
oxygen-scavenging functionality, an oxygen barrier liner made up of
high-density polyethylene (HDPE), or a liner polymer from a different
manufacturer had no significant effect on the composition of volatiles
in beers after prolonged storage of 55 days at room temperature;
however, significantly higher amounts of myrcene and limonene were found
in the oxygen barrier-type crown cork, while all other closures tested
contained similar amounts. Can coatings were demonstrated to absorb hop
volatiles in a similar pattern as crown cork closures but to a lesser
extent. The highest proportion of terpenes was still found in the can
coating, but significantly higher percentages of myrcene were found in
the beers. A short exposure time to the packaging material already
yielded a high migration of certain compounds, which alters the original
balance of the flavor compounds and, thus, results in flavor losses and
flavor deterioration. This is the first time that the scalping of hop
volatiles in beer systems was described by Fick’s second law of
diffusion. Outcomes from this study point to the importance of scalping
in beer systems and, therefore, will help improve closures and to
“rethink” experimental designs when assessing hop aroma.
From 1975 to 1981 Frank-Jürgen Methner studied brewing science at
the Technische Universität Berlin (TU Berlin). After graduating with a
diploma-engineer, he worked as an operating supervisor at the Schlösser
Brauerei in Düsseldorf, Germany. From 1982 to 1986, Frank did his degree
dissertation at the TU Berlin, titled “Aroma Formation of Berliner
Weissbier with Special Focus on Acids and Esters,” and worked on
research projects. From 1987 to 2004, he was director at the Bitburger
Brauerei, Bitburg, Germany, with responsibilities in R&D, as well as
QA. Since 2004, Frank has held the chair of brewing science at TU
Berlin.
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